An insurgency can end through negotiation and the satisfaction of certain, often predictable, political aims, such as the withdrawal of foreign military forces, or the granting of autonomy. But ISIS does not demand the withdrawal of foreign military forces—quite the contrary, it has expressed the wish to draw foreign armies into its territory, and to export its military force beyond Syria and Iraq. It does not call for the simple granting of autonomy to its members and supporters in Syria and Iraq—it works to end the autonomy of others in both places, and far beyond, not least through ethnic cleansing and the worldwide export of wanton violence. If ISIS were willing to be satisfied by, say, a joint Sunni Arab zone in Syria and Iraq, governed under a perverted form of Islamic law, then one could talk about the possibility, if not the laudability, of negotiation. But the point of ISIS is precisely that it cannot be satisfied without forcibly changing the very contours of the current international order.
Powell suggests that “even if some of the hardline leaders of ISIS … want nothing less than their full demands (including ushering in the apocalypse), other more moderate leaders will, under military pressure, be prepared to settle for more modest gains.” Negotiations should, in his view, “strengthen those moderates’ positions in ISIS’s internal discussions.” Indeed, it is possible to “peel away” ISIS members, as evidenced by the number of occasions on which ISIS recruits have defected after realizing that the group isn’t all it is cracked up to be. But those “moderate” former members are essentially irrelevant to the group (unless of course they’re targeted for execution); they are not about to influence discussions within ISIS, much less take it over. These defections have in no way pushed the group toward being more palatable to international norms—in fact ISIS’s continued ability to recruit depends in part on the leadership’s very refusal to accept “nothing less than their full demands.” If ISIS remains true to its principles, that’s also the reason the world can accept nothing less than the group’s full defeat.